Head to head
Mounjaro vs Wegovy
Two weekly injections, both licensed in the UK for weight management. Here is what actually separates them — and why the headline figures you have seen set against each other are not a fair race.
Tirzepatide
Mounjaro
GLP-1 + GIP
Acts on two receptors
- One injection a week
- Six strengths, 2.5mg to 15mg
- Four to five months to the top strength
- 15mg is a maximum — many settle below it
- Needles usually supplied separately
Semaglutide
Wegovy
GLP-1
Acts on one receptor
- One injection a week
- Five strengths, 0.25mg to 2.4mg
- Around four months to the maintenance dose
- 2.4mg is a maintenance dose — where treatment settles
- Needle built into the pen
22.5% against 15% is not a race
Both figures are real, and both get quoted side by side as though one beat the other. That is where it goes wrong. They come from two separate trials, run years apart, with different participants — not from one study that gave each group a different medicine and compared them. The durations differ too: 72 weeks against 68. And both are averages, with individual results inside each trial varying widely in both directions.
The honest summary is narrower than the one usually offered: on the evidence available, tirzepatide produces greater average weight loss. How much greater, for you specifically, is not something a seven-point gap between two trials can tell you.
Where the difference is real
The mechanism
Tirzepatide acts on GLP-1 and GIP; semaglutide on GLP-1 alone. A genuine distinction rather than a marketing one — but acting on two receptors is a description, not a verdict.
What the top dose means
Wegovy has a maintenance dose treatment aims to settle at. Mounjaro has a maximum many people never reach. That changes the shape of treatment — and which strength you should compare on price.
Side effects
Broadly the same in kind — mostly gastrointestinal, worst early and after each increase. Which is why switching between the two is often not the fix people hope for.
Which should you choose?
We are not going to answer that, and you should be wary of any comparison site that does. Which medicine is appropriate depends on your medical history, what else you take, what you have tried before, and what is actually available — none of which a web page knows.
It is a prescriber’s decision, and in practice it is often narrowed by supply before preference comes into it. What we can do is make that conversation better.
Take these to your consultation
- Given my history, is one more suitable than the other for me?
- Does anything else I take interact with either?
- What strength would I realistically aim for, and how long would that take?
- If side effects are difficult, what would you try before stopping?
- How would I reach someone if there is a problem between orders?
Compare at the strength you would actually be on
We have deliberately not printed prices on this page. UK providers price each strength separately and change what they charge, so a figure typed into an article is out of date shortly after it is written — and comparing a starting dose of one against a maintenance dose of the other is not a comparison at all. Each listing below shows the complete cost at that strength, including consultation and delivery fees, alongside the date it was last checked.
Sources
- Summaries of product characteristics for both products, electronic medicines compendium
- Jastreboff AM and others, SURMOUNT-1, New England Journal of Medicine, 2022
- Wilding JPH and others, STEP 1, New England Journal of Medicine, 2021
PenCompare is an independent comparison platform, not a pharmacy or a prescriber. This page is information, not medical advice, and not a recommendation to take any medicine. Both products are prescription-only.